The present invention relates to accumulators for use with high pressure hydraulic systems such as used in oilwell blowout prevention control systems. More particularly, the present invention relates to float systems for an accumulator wherein a hollow float is movable along a vertical guide rod within the accumulator. The float is used to close a shutoff valve at the bottom of the accumulator to prevent the escape of precharged gas.
When a new accumulator is moved from a point of manufacture to a point of installation or a used accumulator is moved from one site to another, it is often necessary to tilt the accumulator when removing it from its mounting and loading it onto a vehicle. Such tilting of accumulators often causes the problem of flooding of the hollow float. Specifically, fluid enters the float through the vent tube. The vent tube assures that the pressure within the hollow float is the same as the pressure on the outside of the float. Once the float has been flooded it sinks to the bottom of the accumulator. The only way of repairing the accumulator is to disassemble the tank and repair or replace the float. Such repair is a complex and expensive undertaking.
In order to prevent disabling of the accumulator by flooded floats, various valve actuator systems have been proposed. One system employs a collapsible float which can be removed from an enlarged opening in the bottom of the accumulator whenever the float floods.
In another system, an expanding bladder is used instead of a float The expanding bladder increases in size as the accumulator empties. When the bladder is large enough, it contacts the valve at the bottom of the accumulator thus causing the valve to close.
Yet another system is described in U.S. Pat. No. 4,294,288 to Murthy. In this system, a rotating accumulator float is weighted on one side. When the accumulator is tilted the fluid level is at an angle with respect to the float travel guide rod. The weight in the float causes the float to rotate around the guide rod thus moving the vent outlet above the level of the fluid in the accumulator. When the accumulator is upright the float engages the float travel guide rod with a moment arm caused by the uneven distribution of weight in the float. Eventually this moment arm will cause the float or the guide rod to wear. This wearing effect will reduce the ability of the float to travel up and down the guide rod and eventually render the accumulator unservicable. Additionally, if the accumulator is tilted on an axis passing through the weight, the float may not rotate with sufficient speed to prevent fluid from entering the vent tube and flooding the float.
There is therefore a need in the art to provide a float system for a ball type accumulator which will remain unflooded when the ball type accumulator is tilted or moved. Such float system should not place a moment arm on the float travel guide rod and should not require any undue movement of the float with respect to the vertical guide rod. Additionally, such float should respond quickly to any tilting of the accumulator.